Ion engine

ABSTRACT

In an ion engine wherein neutral gas enters into a gas discharge chamber in which it is fully ionized, wherein said gas discharge chamber is a part of a high-frequency resonator for effecting ionization of the neutral gas, having an electrostatic accelerating system closing off one end of said chamber and operating to extract ions from the gas discharge and accelerate same to create an accelerated ion beam and further having means for neutralizing the accelerated ion beam there is provided the distinctive feature of positioning the accelerating system at the open end of the high-frequency resonator.

1 1 Feb. 18,1975

1 1 ION ENGINE [75] Inventor: Alfred Bahr, Munich, Germany [73]Assignee: Messerschmitt-Bolkow-Blohm GmbH, Munich, Germany 22 Filed:Apr. 18.1973

21 App1.No.:352,176

[30] Foreign Application Priority Data Apr. 21, 1972 Germany 2219545[52] U.S. Cl 60/202, 3l3/231.3, 313/23l.7. 313/362, 313/363, 315/39.315/1l1.3. 315/11 1.5 [51 Int. Cl.. F03h U00. HOSh 1/18 5 Field ofSearch 60/202; 313/63, 231; 315/39, 111; 328/233 [56] References Cited Iv UNITED STATES PATENTS 3,110,842 11/1963 Hilliard 315/39 3,418,20612/1968 Hall et a1. 313/63 3,449,618 6/1969 Gallagher 313/63 X 3,450,9316/1969 Feinstein ct a1. 313/63 X 3,466,554 9/1969 Giordano 313/63 X3,476,968 11/1969 Omura 313/231 X 3,571,734 3/1971 Consoli et a1 313/63X 2/1973 Bain m til... 313/63 x 7/1973 Margosian et a1. 313/63 X OTHERPUBLICATIONS Loeb, H. W., Recent Work on Radio Frequency Ion Thrusters",Journal of Spacecraft, May, 9171, pp. 494-500/ PrimaryE.raminer--Carlton R. Croyle Assistant Examiner-Robert E. GarrettAttorney, Agent, or FirmW00dhamS, Blanchard and Flynn [57] ABSTRACT Inan ion engine wherein neutral gas enters into a gas discharge chamber inwhich it is fully ionized, wherein said gas discharge chamber is a partof a highfrequency resonator for effecting ionization of the neutralgas, having an electrostatic accelerating system closing off one end ofsaid chamber and operating to extract ions from the gas discharge andaccelerate same to create an accelerated ion beam and further havingmeans for neutralizing the accelerated ion beam there is provided thedistinctive feature of positioning the acceleratingsystem at the openend of the high-frequency resonator 7 Claims, 3, Drawing Figures IONENGINE FIELD OF THE INVENTION The invention relates to an ion enginehaving a fuel conveying system and a gas discharge chamber into whichfuel enters in gaseous form and which is part of a high-frequencyresonator for effecting ionization of the gaseous fuel. The engine isfurther provided with an electrostatic accelerating system which in partdefines the gas discharge chamber and extracts ionized gaseous fuel fromthe gas discharge chamber and accelerates same to create an acceleratedion beam and is also provided with a device for neutralizing theaccelerated ion beam.

BACKGROUND OF THE INVENTION This type of an ion engine is described inmy copending application Ser. No. 190,981, filed Oct. 20, 1971, now U.S.Pat. No. 3,757,518, issued Sept. 11, 1973, in which arrangement the gasdischarge chamber is closed off by a metallic grid plate at which theelectrical highfrequency field forms a node. Thus, Lorentz forces act onthe ionized gaseous fuel in the gas discharge chamber for acceleratingsaid fuel to the grid plate whereby through the so generated axialvelocity component of the ionized fuel on the grid plate a highercurrent density is achieved than is the case in conventionalhighfrequency ion engines, which, for example, are described in H. W.Loeb, State of the Art and Recent Developments of the Radio FrequencyIon Motors, AIAA Paper No. 69-285. Also the ion engine according to theaforementioned US. Pat. No. 3,757,518 is constructed in a simple andsturdy manner since it can be built almost entirely of metal and sincein addition the electronic arrangement is simple. In addition thehighfrequency losses are small in this engine because the entire highfrequency energy is contained within the closed resonator and cannotradiate outwardly as in the known engine which operates with aninduction coil wound around the entire discharge chamber.

Of course, Lorentz forces can become effective in the gas dischargechamber only below a certain critical pressure at which the free pathlength of the charge carrier exceeds at least some cycles of oscillationof the electrical field. At higher pressures, and accordingly also athigher gas densities, the collisions within the gas discharge become,however, so frequent that the free path length of the charge carrierbecomes too small and the Lorentz forces are no longer effective.

SUMMARY OF THE INVENTION The purpose of the invention is the furtherdevelopment of the described high-frequency ion engine while at the sametime maintaining the simple and sturdy construction ofthe entire engine.In particular, it is the purpose of the invention to substantiallyincrease the density of the gas discharge particularly adjacent to theaccelerating electrode system in order to increase the thrust.

This purpose is attained according to the invention by arranging theaccelerating electrode adjacent to the open end of the high-frequencyresonator.

Thus the standing electrical wave within the highfrequency resonatorforms at the end of the gas discharge chamber adjacent to theaccelerating electrode a loop of oscillation and not, like in theabovedcscribed ion engine, an oscillation node. Thus the internalacceleration effect which is based on Lorentz forces in the gasdischarge and accordingly the thereby additionally obtainable currentdensity on the grid plate here intentionally is relinquished.Contrastingly, in the case of the invention, the greatest possibleenergy is transmitted for the ionization of the gaseous fuel within thegas discharge chamber at the open end of the resonator, so that in thevicinity of the loop of oscillation, thus at the accelerating electrode,the density of the gas discharge is at its maximum. In this manner, thecurrent density of the accelerated ion beam is also increased so thathigh thrust can be produced with the ion engine according to theinvention.

The construction of the ion engine of the invention is simple and sturdybecause the high-frequency resonator consists entirely of metal and isenergized, for example, by a common planar triode without requiring anygreat amount of electronic components.

BRIEF DESCRIPTION OF THE DRAWING Further details of the invention willbe disclosed in the following description in connection with thedrawing, in which:

FIG. I is a first exemplary embodiment of a highfrequency ion engineaccording to the invention;

FIG. 2 is a further exemplary-embodiment of an ion engine according tothe invention and FIG. 3 illustrates the shape of the standingelectrical high-frequency wave H within the ion engine.

DETAILED DESCRIPTION An ion engine 1 is built of two metallic hollowcylinders 2 and 3 which are arranged concentrically to one another andthe lengths of which correspond to half of the wavelength of anelectrical high-frequency field. This electrical high-frequency field isproduced by means of a coaxial planar triode 4 which is located at oneopen end of the k/Z-resonator formed by the concentrical metallic hollowcylinders 2 and 3. The planar triode together with the A/Z-arrangementof the hollow cylinders 2 and 3 and a DC-power supply 41 forms anoscillator circuitry, for example, the known Colpitt circuitry, andconsists of a cathode 43 which is heated by a heating system 42, a grid44 which is connected through an isolating capacity 45 to the innerhollow cylinder 3 and an anode 46. Further, for cooling the anode 46, aplurality of radiator fins 47 are arranged on the periphery of the outerhollow cylinder 2, which radiator fins 47 are used to dissipate thewaste heat from within the anode 46.

A gas discharge chamber 7 is defined on the end of the high-frequencyresonator opposite the planar triode 4 by a wall 5 of dielectricmaterial, preferably of quartz, and by a so-called grid plate 6 ofdielectric material, preferably quartz and having a plurality ofopenings 61. An annular anode 8 is arranged on the wall 5, with whichanode is associated an accelerating electrode 9 which is electricallyisolated from the high-frequency resonator.

Anode 8 and accelerating electrode 9 are electrically connected througha source 10 of dc. voltage, as a battery, which delivers an acceleratinghigh voltage.

When the thus-described high-frequency resonator is energized, theelectrical high-frequency field forms a standing electrical wave of halfof a wavelength, the loops of oscillation of which lie each at the twoopen ends of the high-frequency resonator and the oscillation nodes ofwhich lie in the center of the highfrequency resonator, as shown in FIG.3.

An evaporator 11 is arranged inside the inner hollow cylinder 3, intowhich evaporator liquid mercury is fed from any suitable reservoir, notillustrated, through a supply line 12. The evaporator 11 and the supplyline 12 are held in the inner hollow cylinder by electrically insulatingsupport elements l3, l4 and 15. The liquid mercury is evaporated in theevaporator 11 and is fed through multiple channels 16 to the gasdischarge chamber 7 wherein the gaseous mercury is ionized by thehigh-frequency field. As can be seen from FIG. 3, the alternating fieldforms a loop of oscillation near the grid plate 6, so it is possible towithdraw the maximum energy for effecting ionization of the gasparticles from the high-frequency alternating field in this region.Consequently the density and the intensity of the gas discharge will bethe greatest at the grid plate.

Since a focusing effect is achieved in the gas discharge by the gridplate 6, as is known, the positive mercury ions are extracted from thegas discharge chamber 7 and are accelerated forming an ion beam by theaccelerating electrode 9 which is at a negative potential with respectto the anode 8. It can within the scope of the invention be advantageousif, as is already known, a decelerating electrode is arranged followingthe accelerating electrode. This arrangement is, of course, notillustrated in the figures.

Since only the positive mercury ions are extracted from the gasdischarge chamber 7, the electrons which are generated during theionization procedure and remain in the gas discharge chamber 7 must beremoved from the gas discharge chamber 7, in order to avoid a negativecharge on the ion engine. This is advantageously accomplished by anarrangement already described in the earlier mentioned U.S. Pat. No.3,757,518 of applicant.

For this purpose, the gas discharge chamber 7 has openings 17 on its endfacing the grid plate 6, which openings connect the discharge chamber 7to a tubeshaped hollow member 18. Same extends through an opening 19 ofthe accelerating electrode 9 and is also provided with openings 20 onits end remote from the ion engine 1. A small portion of the mercurywhich is in plasma condition in the gas discharge chamber 7 is urgedthrough the openings 17 into the hollow member 18 and further throughthe openings 20 towards the accelerated ion beam leaving theaccelerating electrode 9 and forms thus a plasma bridge between the gasdischarge chamber and the accelerated ion beam. The electrons whichremained in the gas discharge chamber 7 are drawn into the acceleratedion beam through this plasma bridge, because said ion beam provides apositive anode for the electrons. In this manner the ion beam isneutralized and a negative charge on the ion engine 1 is prevented. Ofcourse, the neutralization of the ion beam can also take place by meansof a conventional hollow cathode.

A second embodiment of the invention which is illustrated in FIG. 2differs from the described first embodiment only in that a differentconstruction is shown for the high-frequency resonator. At the point atwhich in the first exemplary embodiment the standing wave ofhigh-frequency field forms an oscillation node, the presenttl2-resonator is interrupted by a metallic partition wall 21 which isarranged between the hollow cylinders 2 and 3. In this manner twoconnected M4- resonators are created; the one of the )t/4-resonatorswhich contains the planar triode 4 serves thereby as a high-frequencygenerator producing the highfrequency energy which is coupled by meansof a coupling loop 22 into the second )t/4-resonator which contains thegas discharge chamber 7 (for coupling to cavity resonators seeElectronic and Radio Engineering, fourth edition, by Frederick EmmonsTerman, McGraw-Hill Book Company, Inc. (I955), at Page 164.). Operationand distribution ofthc high-frequency alternating field are in thisexemplary embodiment. the same as in the first exemplary embodiment sothat in the figure for same the parts are shown with the same referencenumerals.

An ion engine according to the invention is distinguished as can be seenfrom the above by a sturdy and simple construction; at the same timethrough the specific construction of the ion engine as a part of an openhigh-frequency resonator a high gas discharge density is obtained in thegas discharge chamber so that a considerable thrust can be achieved withthis ion engine.

Although a particular preferred embodiment of the invention has beendisclosed above for illustrative purposes, it will be understood thatvariations or modifications thereof which lie within the scope of theappended claims are fully contemplated.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In an ion engine with means defining a fuel conveying system andmeans defining a gas discharge chamber into which fuel enters in agaseous form, means defining a high frequency resonator, said gasdischarge chamber being part of said high-frequency resonator foreffecting ionization of the gaseous fuel, means defining an acceleratingelectrode system at one end of said gas discharge chamber for extractingionized gaseous fuel from said gas discharge chamber and acceleratingsame thus creating an accelerated ion beam and means for neutralizingthe accelerated ion beam, the improvement comprising said acceleratingelectrode being arranged adjacent to said open end of said highfrequencyresonator. said high-frequency resonator producing a standing wavehaving a node in the center of said high-frequency resonator and anoscillation loop at said open end.

2. The improvement according to claim 1, wherein said high-frequencyresonator is a A/Z-resistor wherein A is the wave length of standingwave.

3. The improvement according to claim 2, wherein said h/Z-resonatorconsists of two coupled M4- resonators, of which only one is used forproducing the high-frequency alternating field and is connected to theother resonator by coupling elements.

4. The improvement according to claim 1, wherein said open end of saidresonator which defines said gas discharge chamber is closed by a gridplate made of dielectric material.

5. The improvement according to claim 4, wherein said dielectricmaterial is quartz.

gizing said resonator at its given frequency and producing, in saidhigh-frequency resonator, a standing electrical wave having a nodelocated intermediate the ends of said resonant chamber; and dielectricmeans mounting said acceleration electrode on said cylindrical walladjacent the open end of said high-frequency resonator.

7. The improvement according to claim 6, wherein said high-frequencyresonator is a A/Z-resonator.

wherein is the wave length of the standing wave.

1. In an ion engine with means defining a fuel conveying system andmeans defining a gas discharge chamber into which fuel enters in agaseous form, means defining a high frequency resonator, said gasdischarge chamber being part of said high-frequency resonator foreffecting ionization of the gaseous fuel, means defining an acceleratingelectrode system at one end of said gas discharge chamber for extractingionized gaseous fuel from said gas discharge chamber and acceleratingsame thus creating an accelerated ion beam and means for neutralizingthe accelerated ion beam, the improvement comprising said acceleratingelectrode being arranged adjacent to said open end of saidhigh-frequency resonator, said high-frequency resonator producing astanding wave having a node in the center of said high-frequencyresonator and an oscillation loop at said open end.
 2. The improvementaccording to claim 1, wherein said high-frequency resonator is a lambda/2-resistor wherein lambda is the wave length of standing wave.
 3. Theimprovement according to claim 2, wherein said lambda /2-resonatorconsists of two coupled lambda /4-resonators, of which only one is usedfor producing the high-frequency alternating field and is connected tothe other resonator by coupling elements.
 4. The improvement accordingto claim 1, wherein said open end of said resonator which defines saidgas discharge chamber is closed by a grid plate made of dielectricmaterial.
 5. The improvement according to claim 4, wherein saiddielectric material is quartz.
 6. In an ion engine having means defininga discharge chamber closed off by a perforated wall, a gaseous fuelsupply system communicating with the discharge chamber and supplyingthereto electrically neutral fuel in gaseous form, a high-frequencygenerator operable to ionize the gaseous fuel in the discharge chamber,a perforated acceleration electrode mounted in electrically insulatedrelation, in outwardly spaced relation to the perforated wall of thedischarge chamber and pulling the ionized fuel out of the dischargechamber and accelerating the ionized fuel electrostatically to create anaccelerated ion beam, and means operable to neutralize the acceleratedion beam, the improvement comprising said discharge chamber forming partof a high-frequency resonator having a cylindrical wall closed at oneend by said perforated wall, said resonator containing saidhigh-frequency generator and said fuel supply system; saidhigh-frequency generator energizing said resonator at its givenfrequency and producing, in said high-frequency resonator, a standingelectrical wave having a node located intermediate the ends of saidresonant chamber; and dielectric means mountIng said accelerationelectrode on said cylindrical wall adjacent the open end of saidhigh-frequency resonator.
 7. The improvement according to claim 6,wherein said high-frequency resonator is a lambda /2-resonator, whereinlambda is the wave length of the standing wave.